Women living within about a mile of fields, farms or other sites that use agricultural pesticides have a 60% higher risk of delivering a child with autism spectrum disorder or other developmental delays. Women in their second and third trimesters appear to be at the highest risk, according to the study.

The study, published Monday in the journal Environmental Health Perspectives, strengthens the evidence linking developmental disorders with exposure to pesticides during gestation, researchers said.

“While we still must investigate whether certain sub-groups are more vulnerable to exposures to these compounds than others, the message is very clear: Women who are pregnant should take special care to avoid contact with agricultural chemicals whenever possible,” lead author Janie Shelton said in a statement.

In an interview with the Los Angeles Times, Shelton said regulators should consider testing pesticides to see if they alter the nervous system during development.

“It is not a requirement of getting a pesticide approved,” she said. “Instead of putting the onus entirely on women thinking of getting pregnant, I think the public should consider that regulators require this kind of testing.”

The study focused on commercial pesticides at multiple sites throughout California and linked the data to addresses of the 1,000 participants in the Northern California-based Childhood Risk of Autism from Genetics and the Environment study, which gathers information on children between 2 and 5 diagnosed with autism or other developmental delays.